The invention relates in general to a device for the drainage of cerebrospinal fluid and in particular to a drainage system comprising a fluid (liquor) drainage line, a fluid pressure sensor, and a pump for pumping out said fluid.
In patients with hydrocephalus and/or increased intracranial pressure the surplus cerebrospinal fluid (liquor cerebrospinalis or in abbreviated form “liquor”) is either drained into any body cavity or into the blood by internal drainage devices or drained to the outside by external drainage devices. A liquor drainage arrangement normally consists of a brain catheter, which is inserted into the intracranial cavity (ventricle) to be treated through a hole in the skull and connected to a drainage line to the outside or to the desired body cavity or vein.
The formation of cerebrospinal fluid is about 500 ml/day, the pressure of the liquor in the lumbar region of the brain and in the brain ventricles having a constant value within defined limits. The drainage device is to be used in the treatment of hydrocephalus to produce reduced pressure of the cerebrospinal fluid in the patient's skull, wherein the lower pressure of the cerebrospinal fluid (liquor pressure) aimed at during treatment should be below the blood pressure of the brain.
An external liquor drainage arrangement is known, for example, from DE 296 21 904 U1, in which a so-called balancing chamber, where the drained fluid is collected and its volume determined, is attached to a height-adjustable stand. Owing to the sensitivity to pressure of the brain, it is extremely important in the drainage of cerebrospinal fluid or liquor to maintain a preset drainage pressure. The balancing chamber of the known liquor drainage arrangement therefore has to be precisely aligned to a specific height in relation to the patient's head. Provided in the liquor line is a pressure measurement converter, which measures the current pressure of the cerebrospinal fluid in the liquor line. The drainage pressure and therefore the hydrostatic pressure in the drainage line and the balancing chamber should, thus, not exceed or drop below specific limit values. If the patient's head position is changed, for example by swiveling the back of the bed, the balancing chamber and the pressure measurement converter must also be adjusted in height, so that on the one hand the pressure measurement is correct and on the other hand the pressure limit values are met.
DE 103 17 308 describes a liquor drainage arrangement which is likewise arranged on a height-adjustable stand, with a balancing chamber fixed to the stand, a liquor feed line connected to the balancing chamber, a pressure measurement converter in the liquor feed line and a positioning device for adjusting the height position of the stand. In the device disclosed in DE 31 27 882 a valve with a specific closing pressure is used to control the process for discharging the liquor. The operating pressure of the valve in the drainage device, thus, corresponds to the desired liquor pressure. Discharge of the cerebrospinal fluid from the ventricles takes place all the time the liquor pressure is above the switching pressure of the valve. DE 693 31 185 discloses monitoring of the pressure with optical sensor means.
U.S. Pat. No. 6,336,924 B1 discloses a liquor drainage arrangement, discharge of the liquor fluid into a collecting container being controlled by a valve which opens at a specific pressure. The liquor can again discharge only on the basis of the difference in the hydrostatic pressure between the brain ventricle and the collecting container and is not actively pumped out. This results in the disadvantage that, with this known liquor drainage system the amount of liquor draining out is also determined by the difference in height between the ventricular catheter and the collecting container. If, for example, the collecting container is arranged at the same height as the inserted ventricular catheter or even above the intraventricular catheter, no or insufficient liquor can drain out, even if there is increased intracranial pressure. Since this known arrangement is an open system when the valve is open, it is not the ventricular pressure which is measured by the pressure sensor attached after the intraventricular catheter, but the pressure in the collecting container. Therefore a pressure measurement in the described structure according to the prior art is possible only when the valve is closed. In addition, volume-controlled drainage is not possible with this known liquor drainage system.
The liquor drainage arrangements known to date have the disadvantage that they have a complicated structure and adaptation of the discharge amount to changed pressure circumstances in the liquor feed line have to be performed either by mechanical means or manually. This is also associated with corresponding inaccuracies.